High‐Power Mid‐IR Few‐Cycle Frequency Comb from Quadratic Solitons in an Optical Parametric Oscillator

Abstract

Powerful and efficient optical frequency combs in the mid-infrared (MIR) spectral region are highly desirable for a broad range of applications. Despite extensive efforts utilizing various techniques, MIR frequency comb sources are still lacking power, efficiency, or bandwidth for many applications. Here, we report the generation of an intrinsically locked frequency comb source centered at 4.18 µm from an optical parametric oscillator (OPO) operating in the simulton regime, in which formation of purely quadratic solitons lead to enhanced performance. We show advantages of operation in the simulton regime in direct experimental comparisons to the conventional regime, which are also supported by simulation and theory.We achieve 565 mW of average power, 900 nm of instantaneous 3-dB bandwidth, 350% of slope efficiency, and 44% of conversion efficiency; a performance that is superior to previous OPO demonstrations and other sources in this wavelength range. This work opens a new avenue toward MIR frequency comb generation with high power and efficiency and suggests the great potential of soliton generation based on quadratic nonlinearity in the MIR spectral region.

Mid-infrared cross-comb spectroscopy

“…The improvement of any of these elements can be exploited to better the performance and capability of CCS. First, in the past decade, there has been impressive progress in the generation of high-power (>100 mW) MIR FCs [13][14][15][16][17][18][19] . However, MIR DCS has not taken full advantage of this progress yet, as MIR detectors typically saturate at ~1 mW.…”

“…Conversely, CCS can reap the full benefits of more powerful target pulses as saturation is not a main problem. Although the target pulse used in our experiment is already among the FCs with the highest power in its wavelength region, it can still be improved 13 and enhance the CCS performance.…”

“…Third, a 1-mm commercial bulk PPLN crystal with a poling period of 29.52 µm is used in our experiment as the nonlinear medium, which provides an upconverted MIR bandwidth of 4080 nm -4530 nm and limits the upconversion efficiency and bandwidth. The total 9 different poling periods of the crystal are expected to provide a combined SFG bandwidth of 2400 nm to 5200 nm, which can cover the whole bandwidth of our MIR target FC 13 (3500 nm to 5200 nm, see Supplementary Fig. 2).…”

“…To experimentally demonstrate CCS in the MIR, we conduct a measurement of atmospheric carbon dioxide (CO 2 ) around 4.25 µm (2349 cm −1 , antisymmetric stretching mode ν 3 ). The target FC consists of 50-fs pulses centered at 4.2 µm with 500 mW of average power provided by two-stage cascaded efficient half-harmonic optical parametric oscillators (OPOs), which are intrinsically phase locked to the pump frequency comb (a mode-locked Yb-fiber laser) at 1 µm 13 . The local FC is a NIR FC centered at 1560 nm (a mode-locked Er-fiber laser) with a 100-nm (400-cm −1 ) FWHM bandwidth, 100-fs pulse width and a 200-mW average power (Menlo Systems FC1500-250-WG).…”

“…Additionally, the sensitivity can still be limited by detector saturation. Therefore, although significant progress has been made toward broadband and high-power (>100 mW) MIR frequency combs [13][14][15][16][17][18][19] , the MIR DCS does not yet take full advantage of such sources since typical MIR detectors saturate at ~1 mW. Recently, some works have been demonstrated to alleviate the background issue by linear interferometry 20,21 .…”